Disagree. Surely the drop in PC sales is not due only to W8, but it is a significant factor.

No it's not. People do not buy PC bc OS, they buy PC when there is a need for it.

Very few buyers (individual or corporate) face a clear-cut "need". "Yes we need it or no we don't" - rarely is it that simple.

For corporates there are often many factors to be considered: cost of carrying on with existing kit (or without any kit, as the case may be), cost of buying new kit. And included in the costs are cost of training and any efficiency gains and losses (including extra or reduced help desk costs). This will include cost of retraining for W8, cost of re-engineering support services for W8, cost of rolling out new software... The move from XP to W7 brought clear gains to enterprises in reduced support and maintenance costs. It's not clear that's the case for W8, and unless you pre-install Start8 (or in some other way suppress Metro as far as possible) the roll-out costs in supporting users are going to be significant.

Consumers make computer purchase decisions based much more on want than need, and W8 appears to be reducing the "want" for some people. We can argue how many "some" is, but remember that gadget-loving techy users (I admit I'm one) number well under 10% of computer users, probably well under 5%.